These are errors made by students I taught at Guangdong University of Foreign Studies in Guangzhou, China. The students were at a high-intermediate to advanced level.
The timer gives you 15 seconds to find the answer. It notes your errors but it only shows you the correct answers at the end.
If you don't use the timer you see the correct answers immediately and in many quizzes you can click on Another example to see a similar word or sentence.
In fact, even if you know the correct answer, it is sometimes useful to click on the wrong one to get more detailed feedback with further examples of usage.